Belgian Foreign Minister Willy Claes whistles as he conducts the National Orchestra of Belgium with Toots Thielmans in a 1994 concert. The harmonica titan initially made his name as a guitarist. (PIERRE THIELMANS/Associated Press)

His gait is unsteady and his broad face thinning with age. But for nearly two hours this summer, Jean “Toots” Thielemans — who more than half a century ago elevated the harmonica to the pinnacle of the jazz world — sat erect in a straight-back chair and, in his soft and slightly accented English, talked about his music, his instrument and his life.

Thielemans, who is considered a national treasure here, stopped touring two years ago after a 70-year career and now rarely leaves his art-filled home in the Belgian village of La Hulpe, just a couple of miles from Waterloo, about a half-hour drive from Brussels.

His major ailment is age, something his wife, Huguette, constantly reminds him is not bad for 93. “I can’t see well. I can’t hear well,” says Thielemans, cradling his harmonica, which he repeatedly uses to show a visitor a particular chord or run. “I don’t know the name,” he says, about the scale he just played, which has his signature sound. “It’s sort of a double diminished, not yet hip, but on the way to hip.”

Thielemans is preeminently a jazz musician — he’ll tell you the chromatic harmonica just happens to be his instrument, but “it could be a broomstick or a tuba” — and he’s recorded with many of the music’s most illustrious figures, from Oscar Peterson to Benny Goodman, Pat Metheny to Quincy Jones, Shirley Horn to Dizzy Gillespie. But he’s never shied away from commercial gigs; his harmonica is instantly recognizable in the theme song to “Sesame Street” and “Midnight Cowboy” and innumerable other film scores. Toots whistled the Old Spice deodorant commercial in the 1970s and ’80s, and he wrote the jazz standard “Bluesette,” which he originally played on the guitar while whistling the melody an octave higher.

“Toots was happy to play ‘Bluesette’ every night,” recalls Fred Hersch, who was Thielemans’s regular pianist in the early and mid-1980s. So much so that his much younger sidemen would sometimes chafe at the predictability of it all and start goofing on the rhythm and melody, trying to throw Thielemans off. “He liked a good practical joke,” Hersch says. “And when he laughs, he can’t play.”

Thielemans, who is also an accomplished guitarist, holds a singular place in the jazz pantheon: He has dominated the chromatic harmonica in a way that is unimaginable for any other instrument. It’s not simply his uncanny improvisational skills; it’s also his unrivaled ability to pull a certain tone, a certain sweet sadness, out of its thin brass reeds.

Of course, there are a dozen or more world-class jazz chromatic harmonica players on the scene today — in no particular order, there’s Swiss-born Gregoire Maret, Frenchman Olivier Ker Ourio, Antonio Serrano from Spain, Britain’s Philip Achille, Hendrik Meurkens, who was born in Germany but now lives in New York, and Boston’s Mike Turk.

None of them, however, quite matches Thielemans.

Bruno Castellucci, who played drums with Thielemans for some 40 years, remembers a harmonica convention in Trossingen, Germany, where Hohner, the famous harmonica maker, was founded in 1857. “Larry Adler was there, everybody was there,” says Castellucci, referring to the instrument’s first superstar soloist, who played mostly classical music and became famous in the 1930s.

“But I tell you something. When Toots played, it was like . . . .” Castellucci, sitting at an outdoor cafe in Brussels, pauses. “I have goose pinches to think about it,” he adds, meaning goose bumps. “It was like, you see 10 good alto [saxophone] players and then Charlie Parker comes and plays a tune. That’s the end. Goodbye. Finished. There’s no other way.”

There are two basic harmonicas. The smaller, diatonic harmonica, familiarly known as a blues harp, plays an abbreviated version of the scale that emphasizes the tonic and dominant seventh notes, and includes notes that are easy to “bend,” providing the classic blues sound that can lower a tone down to the next note and beyond. This is the blues, rock, and country and western harmonica played by everyone from James Cotton to Bob Dylan to Charlie McCoy.

Thielemans uses the larger chromatic harmonica. Like any harmonica, notes are played by blowing and drawing. But unlike the diatonic, the chromatic also has a spring-loaded button, a small slide that shifts a note by half a step, something that allows a three-octave chromatic scale, which includes sharps and flats, to be played.

It’s simple to play. But intensely difficult to master.

With almost every other jazz instrument, says saxophonist and chromatic harmonica player Dave Schroeder, director of jazz studies at New York University, “there’s a thing called muscle memory. You practice something enough and your hands must go there, your fingers just fire off,” he says. “The harmonica is not tactile. It’s a button and 12 holes. It’s easy to get lost.”

Add to that the instrument’s insistence that certain notes must be blown, and others inhaled, something that by definition makes it tough to play the seamless, legato runs so common in bebop and other jazz styles. “In general, you cannot just take any bebop line that Charlie Parker played and play it convincingly,” says Meurkens, who at least a few times during his set this summer at the Tabard Inn managed to do just that. “You have to overcome the ‘in and out,’ and that is very difficult, the instrument just doesn’t allow that.”

“ ‘Jette ce jouet’ — ‘throw that toy away’, get a real instrument,” everyone told him when he first picked up the harmonica as a child, Thielemans recalls. In fact, Thielemans initially made his name as a jazz guitarist, playing a solid-body Rickenbacker 325 that inspired John Lennon in 1960 to go out and buy one himself.

When Thielemans landed in the United States for the first time in 1947, just 25 years old, “I was a real bebopper. I was up to date.” Thielemans had met the jazz photographer Bill Gottlieb during a jam session in Miami, where he had gone to visit his uncle. Gottlieb told him to look him up when he got to New York.

It was the heyday of jazz in New York, and clubs lined 52nd Street and elsewhere. “ ‘Hey guys, I got this guy from Belgium,’ ” Thielemans said, remembering Gottlieb’s introduction. “ ‘What, that’s in Russia?’ they’d ask. It was surprising for them.” Even more surprising was that Thielemans could make the chromatic harmonica work as a bebop instrument. “And so I sat in with Hank Jones, and that was in the Three Deuces, and each week, they’d have another leader, one week, it was maybe J.J. Johnson or with the trumpet player Howard McGhee,” he says.

“My first attention-getter was an arrangement I did on ‘Stardust,’ ” the Hoagy Carmichael tune, that was noticed by Benny Goodman, who added Thielemans to his band during its 1950 European tour. Goodman would feature Thielemans at least once a night on harmonica; indeed, one of Goodman’s live radio broadcasts from that tour was released in 2006, featuring Thielemans playing chromatic harmonica on his ‘Stardust’ arrangement.

Thielemans got his green card in 1951 and became a U.S. citizen six years later (and was forced to give up his Belgian citizenship until 2000, when Belgium’s King Albert II named him a baron.) “He was living in New York, going down to the musicians’ union, busking like everyone else, trying to pick up gigs, playing bar mitzvahs, restaurants,” said Kenny Werner, who was Thielemans’s last regular pianist.

Thielemans was part of the house band on the Jimmy Dean television show in the early 1960s when he struck gold for the second time. “I wrote a two-note song on the guitar — I had just done ‘Bluesette’ and that was getting attention — and the publisher said, ‘Hey, man, we can sell that.’ And the song, I called it “Ladybug”, it reaches Herb Alpert.”

Alpert’s Tijuana Brass was one of the biggest bands of the mid-1960s. The album that included Thielemans’s tune, “Whipped Cream and other Delights” — with an iconic cover featuring a model draped in nothing but a chiffon and whipped cream — sold 6 million copies. “For each LP sold, I got one penny,” says Thielemans, recalling how he made enough money to buy a house on Montauk and an apartment in Manhattan.

Thielemans had a brain hemorrhage in 1981, just shy of 60, which left him with little strength in his left hand and reduced his guitar playing to just a couple of tunes per show. By then, he had already reestablished his jazz bona fides, cutting albums with pianist Bill Evans and Weather Report bassist Jaco Pastorius, among other leading jazz figures of the day.

As Thielemans moved into his 70s and 80s — and still continued to record and tour, with upward of 250 shows a year — his harmonica playing gained a new profundity, admittedly a word not normally associated with the instrument. “I can’t play bebop now,” Toots told the Dutch journalist René Steenhorst in an interview for his 90th-birthday celebration. But he told Steenhorst, “All those fast notes didn’t make me that popular anyway. It’s much better now. I actually play the main line of a tune now. I say more with less.”

Thielemans made his final recording in 2012 during his 90th-birthday tour; last summer, at 92, he performed in public for the last time at his beloved Jazz Middelheim festival in Antwerp.

“So many changes in my life,” he says quietly. “Thank you for coming. . . . Too much of a rumble in my head,” he adds, clearly tired after reminiscing. He gets up slowly and pronounces the interview over.

Goldman is a freelance writer.